This invention relates generally to a digital sensor of relative position, of the magnetic type, which delivers one reference pulse per revolution, and, more particularly, to a sensor suitable for use in sensor bearings for automobile or industrial applications.
Such sensors can be mounted, for example, in wheel bearings or in steering column bearings of automobiles in order to instruct the navigation systems or to control the trajectory of the vehicle, or in systems for checking and controlling of the position of a robot or of an electric motor. A relative position sensor which moreover delivers an output signal, called a xe2x80x9crevolution tickxe2x80x9d, consisting of a single pulse per revolution, whose length or duration can vary as a function of the devices, is of great interest because this signal can be used as a reference for performing the reinitialization of the processing systems connected downstream from the sensor, and for knowing, by counting up or counting down, the position of a rotor with respect to this reference position.
There are currently relative position sensors of the optical encoder type, which deliver, as output, digital signals, each having a determined number of pulses per revolution and phase shifted by 90 degrees with respect to one another in order to discriminate the direction of rotation. Such signals are represented in FIG. 1, in which they are referenced A and B, and so is a xe2x80x9crevolution tickxe2x80x9d reference signal C, consisting of a single pulse per revolution, whose rising front corresponds to any front of one of the two signals A or B, but whose descending front corresponds to the next front of the other signal. For reasons of reliability, the use of these sensors of optical type is limited to applications executed in environments which are not very severe, with a low level of pollution and a surrounding temperature less than 100xc2x0 C.
There are also sensors of the magnetic type which can function under more severe industrial conditions and which are economically advantageous. They can consist, on one hand, of a multipolar magnetic ring, on which a sequence of north and south poles is provided and which is connected to the mobile part of the component in rotation whose relative position is sought, and on the other hand, of one or more magnetic sensors connected to the stationary part of the component in rotation. These magnetic sensors are, for example, Hall-effect probes or magnetoresistant probes which can be integrated in bearings.
In contrast, in the case in which such a relative position sensor, of the magnetic type, has to deliver a xe2x80x9crevolution tickxe2x80x9d reference information signal, the magnetic tracks, main and xe2x80x9crevolution tickxe2x80x9d tracks, must be sufficiently separated from one another because of the great magnetic influences exerted between them, causing a great space requirement, which is particularly true if one wishes to use the signals coming from the main track in order to increase electronically the resolution of the output signals by known interpolation processes. This disadvantage can prevent such a sensor from being mounted in certain components, in which there is little room.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
In one aspect of the invention, this is accomplished by providing a digital sensor of relative position, which comprises, on one hand, a circular multipolar magnetic ring, on which are magnetized a number of pairs of north and south poles, which are equally distributed, of constant determined angular width, mobile in rotation opposite a stationary magnetic sensor composed of at least two sensitive elements, which are located on a radius (r) of the magnetic ring and a length (d) apart, respectively positioned facing a main track and a xe2x80x9crevolution tickxe2x80x9d reference track, and on the other hand, a device for processing of output signals emitted by the sensitive elements, for providing one reference pulse per revolution of a component in rotation connected with the magnetic ring, wherein, on the magnetic ring, a magnetic pattern is produced from a pair of north and south poles whose transition is different from the transition between other north and south poles of the magnetic ring, and of which the angular width of the north pole is, on one hand, equal to that of the south pole at the main track, and on the other hand, different at the xe2x80x9crevolution tickxe2x80x9d reference track.
According to another aspect of the invention, the magnetic sensor is comprised of three sensitive elements, the first of which faces the xe2x80x9crevolution tickxe2x80x9d reference track, and of which the second and third sensitive elements face the main magnetic track in such a way that one of the two is located on the same radius of the magnetic ring as the first sensitive element a distance (d) apart, and that they are offset with respect to one another along the main track in order to deliver respective signals in quadrature.
According to another aspect of the invention, the magnetic sensor is comprised of two small bars of sensitive magnetic elements, located facing the two tracks, the main magnetic track and the xe2x80x9crevolution tickxe2x80x9d reference track, the two small bars of sensitive magnetic elements being parallel and a length (d) apart, being comprised of a number of sensitive elements, preferably in an even number and an equal number for the two bars, each sensitive element of one bar facing a sensitive element of the other bar.
The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.